Engine restart strategy

ABSTRACT

A method of controlling a vehicle, where the vehicle includes an internal combustion engine and a transmission having a neutral state and an engaged state, includes setting the state of the transmission. The state of the transmission is set as the neutral state or the engaged state based on a restart condition, where the restart condition is one of: (i) a no wheel torque restart condition, and (ii) a wheel torque restart condition. The method additionally includes starting the engine.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/016,102 filed on Jan. 11, 2011, now U.S. Pat. No. 8,744,698, thedisclosure of which is incorporated in its entirety by reference herein.

BACKGROUND

1. Technical Field

The invention relates to an engine restart strategy.

2. Background Art

An engine start/stop system for a vehicle stops the internal combustionengine when the vehicle is stopped, and then starts the internalcombustion engine when the driver requests acceleration. The engine alsomay be started, for example, due to loads on the electrical system ordue to the catalyst temperature being low. For example, the internalcombustion engine may be stopped when the vehicle stops at trafficlights or stops in a traffic jam. This approach is known as staticstart/stop. The stopping of the engine when the engine is not neededimproves fuel economy, and reduces emissions. Although, sometimes, theengine may stay on when the vehicle is stopped because the alternatorneeds to run due to loads on the electrical system, or the engine maystay on for other reasons such as, for example, when the catalysttemperature is too low. In some approaches, fuel economy may be improvedby 3-4% with static start/stop.

It is important that an engine start/stop system functions seamless andtransparent to the driver, with minimal noise, vibration, and harshness.It is also important that when the driver requests torque at the wheelsthrough the accelerator pedal, the time delay for starting the enginemust be minimized.

In one example, the vehicle includes an internal combustion engine and atraditional automatic transmission. The engine torque is transferred tothe wheels though a torque converter and then through the gearbox. Theengine is started via a starter motor. The control system determineswhen to start and stop the engine based upon the driver's actions, thestate of the vehicle and environmental conditions. The engine is startedwith the gearbox in the in gear state.

For the foregoing reasons, there is a continuing need for balancing theneeds for a seamless engine start (minimal noise, vibration, andharshness) and for a fast engine start.

SUMMARY

It is an object of the invention to provide an improved approach toengine restart strategy.

It is a further object of the invention to provide a dual mode enginerestart strategy.

In one embodiment, a method of controlling a vehicle is provided. Thevehicle includes an internal combustion engine, and a transmissionhaving a neutral state and an engaged state.

The method comprises determining a restart condition for the engine; andclassifying the restart condition as one of: (i) a no wheel torquerestart condition, and (ii) a wheel torque restart condition. The stateof the transmission is set based on the restart conditionclassification, and the engine is started.

At the more detailed level, the invention comprehends various additionalfeatures that may be included individually or in various combinations invarious embodiments of the invention. For example, the method mayfurther include determining a shutdown condition for the engine; andstopping the engine in response to the shutdown condition.

In one aspect, the method further comprises detecting an operator actionwhich demands wheel torque. The restart condition is determined inresponse to the operator action. The restart condition is classified asthe wheel torque restart condition. In turn, setting the state of thetransmission further comprises setting the state of the transmission asthe engaged state in response to the wheel torque restart condition.Further, in this aspect, detecting the operator action may furthercomprise detecting the release of the brake pedal or detecting theactuation of the accelerator pedal.

In another aspect, the method further comprises determining a systemcondition which demands engine power without demanding wheel torque. Therestart condition is determined in response to the system condition. Therestart condition is classified as the no wheel torque restartcondition. In turn, setting the state of the transmission furthercomprises setting the state of the transmission as the neutral state inresponse to the no wheel torque restart condition.

The transmission may have an active neutral state and a full neutralstate. In this case, setting the state of the transmission may furthercomprise setting the state of the transmission as the active neutralstate, or as the full neutral state, depending on the situation.

In another embodiment of the invention, a vehicle is provided. Thevehicle comprises an internal combustion engine, a transmission having aneutral state and an engaged state, and a controller. The controller isconfigured to: determine a restart condition for the engine as one of:(i) a no wheel torque restart condition, and (ii) a wheel torque restartcondition. The state of the transmission is set based on the restartcondition classification, and the engine is started.

In another embodiment of the invention, a method of starting a vehicleengine comprises classifying a start condition as one of: (i) a no wheeltorque restart condition, and (ii) a wheel torque restart condition;setting a transmission state based on the restart condition; andstarting the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a powertrain systemconfiguration;

FIG. 2 is a block diagram illustrating a method of the invention forengine restart strategy;

FIG. 3 is a block diagram illustrating further aspects of the invention;and

FIG. 4 is a block diagram illustrating further aspects of the invention.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

The invention comprehends various aspects of an engine restart strategy,particularly useful for an engine start/stop system. Embodiments of theinvention are not limited to any particular powertrain configurations.Examples are described in further detail below.

Balancing the needs for a seamless engine start (minimal noise,vibration, and harshness) and for a fast engine start, in accordancewith the invention, involves classifying restart conditions as one of:(i) a no wheel torque restart condition, and (ii) a wheel torque restartcondition. In more detail, there are several choices the control systemcan make which will affect the balance between engine restart time andNVH. In the following example, the gearbox can be in one of threestates: (1) in gear; (2) active neutral; and (3) full neutral.

In the active neutral state, appropriate clutches are at touching pointsuch that there is zero or near zero torque transfer by the clutches.

In the full neutral state, the clutches are completely disengaged. Thisis how the gearbox operates when the shifter is in the neutral position.

Restarting the engine with the transmission in gear will result in thefastest time to wheel torque delivery. As the engine is started, anytorque through the transmission will result in torque at the wheels.

Restarting in active neutral state will result in zero torque to thewheels, but there will be a minimal delay to wheel torque delivery sinceonly a small amount of additional clutch movement is required totransfer all the torque to the wheels. A challenge with active neutralis correctly determining the touching point. There may be inaccuraciesin this determination.

Finally, restarting in full neutral will guarantee that no torque istransferred to the wheels during the engine restart. This will minimizethe NVH during the restart, but it will require a longer time totransfer torque to the wheels since the clutches need to be engaged.

A problem addressed in embodiments of the invention is how to choose thetransmission state so as to achieve an optimum balance of NVH andminimum time to develop torque at the wheels.

In accordance with the invention, the solution is to differentiatebetween two types of restarts: (i) a no wheel torque restart condition,and (ii) a wheel torque restart condition.

Continuing with the example, a no wheel torque restart (system inducedrestart) happens when something in the vehicle needs the engine started.For example, the engine needs to be restarted for a low battery state ofcharge. In this case, the tradeoff should be shifted towards minimizingNVH since the driver does not need a fast restart.

In a wheel torque restart (driver induced start), the driver interactswith the vehicle (typically through the brake pedal, accelerator pedaland shifter) and the control system determines that torque is requestedat the wheels. Typically this occurs when the driver lifts their footoff the brake pedal and request for creep torque is generated. In thiscase, the tradeoff should be shifted towards fast restart and fasttorque delivery.

In embodiments of the invention, the vehicle differentiates betweenthese two types of engine restarts and modifies the state of thetransmission to optimize NVH versus time to wheel torque delivery.

For no wheel torque restarts, the engine will be restarted with thetransmission either in the active neutral state or in the full neutralstate. The choice of active versus full neutral depends on thetransmission hardware set up and the control system design. For example,some transmissions will be equipped with a transmission auxiliary pumpwhich will maintain transmission line pressure while the engine is off.For a vehicle with a conventional transmission without an auxiliarypump, it will be possible to change the transmission state from fullneutral to active neutral once line pressure is developed from themechanically driven pump.

For wheel torque restarts, the engine will be started with thetransmission in gear. This will minimize the delay from the engine startrequest to the torque delivery at the wheels. Precise control of air,spark and fuel will be required to ensure the torque is deliveredsmoothly through the transmission. If equipped, the torque converterwill provide some isolation between the engine and the wheels.

Embodiments of the invention may be implemented in a variety ofapplications. One example powertrain configuration is described below.

An example powertrain configuration is shown in FIG. 1. A vehiclecontroller 10 includes appropriate logic/controls for implementing anengine start/stop system. An internal combustion engine 12, controlledby controller 10, distributes torque through torque input shaft 14 totransmission 16. The transmission 16 includes a torque output shaft 18drivably connected to vehicle traction wheels 20 through a differentialand axle mechanism 22.

An enhanced starter motor 30 is provided to implement the enginestart/stop system. In general, controller 10 receives input from variousvehicle sensors 40, accelerator pedal 44, brake pedal 46, and shiftlever 48. Controller 10 implements an engine start/stop system by, atappropriate times, stopping engine 12 by halting fueling and startingengine 12 with enhanced starter motor 30 which engages engine 12 througha suitable mechanism 32. The controller 10 may generally implementstart/stop, with one or more of the additional features provided byembodiments of the invention as described in further detail below. Otheraspects of the powertrain system of FIG. 1 may be implemented in a knownfashion as is appreciated by those skilled in the art. Further,embodiments of the invention are not limited to the particularillustrated powertrain configuration. In addition, embodiments of theinvention are not limited to any particular transmission configuration.Although some discussion of an automatic transmission including a torqueconverter and gearbox is provided herein, other arrangements arepossible. For example, a dual clutch transmission is one suchpossibility.

FIG. 2 is a block diagram illustrating a method of the invention forengine restart strategy, in one embodiment. At block 60, a shutdowncondition for the engine is determined. For example, the start/stoplogic may determine a shutdown condition when the vehicle is stopped ata stop light. At block 62, the engine is stopped in response to theshutdown condition.

At block 64, a restart condition for the engine is determined. Forexample, the start/stop logic may determine a restart condition inresponse to a driver request for acceleration. System induced restartconditions are also possible. For example, the restart condition mayalso be determined due to loads on the electrical system or due to thecatalyst temperature being low. At block 66, in accordance with theinvention, the restart condition is classified as one of: (i) a no wheeltorque restart condition, and (ii) a wheel torque restart condition.

At block 68, the state of the transmission is set based on the restartcondition classification. Finally, at block 70, the engine is started.

FIG. 3 is a block diagram illustrating further aspects of the invention,in one embodiment. At block 80, when the engine is stopped, an operatoraction which demands wheel torque is detected. For example, as indicatedat block 82, release of the brake pedal (request for creep torque) maybe detected. In another example, at block 84, actuation of theaccelerator pedal may be detected.

At block 86, the restart condition is determined in response to theoperator action. At block 88, in this case, the restart condition isclassified as the wheel torque restart condition, that is, driverinduced restart. In turn, at block 90, the transmission is set to theengaged state in response to the wheel torque restart condition.Finally, at block 92, the engine is started.

FIG. 4 is a block diagram illustrating further aspects of the invention,in one embodiment. At block 100, when the engine is stopped, a systemcondition which demands engine power without demanding wheel torque isdetected.

At block 106, the restart condition is determined in response to thesystem condition. At block 108, in this case, the restart condition isclassified as a no wheel torque restart condition, that is, a systeminduced restart. In turn, at block 110, the transmission is set to theneutral state in response to the no wheel torque restart condition.

It is appreciated that, in some transmission configurations, there maybe an active neutral state in addition to the full (normal) neutralstate. Accordingly, setting the state of the transmission to the neutralstate (block 110) may, as appropriate, set the state of the transmissionto the active neutral state (block 112) or to the full neutral state(block 114). At block 116, the engine is started.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A method of controlling a vehicle including aninternal combustion engine and a transmission having a neutral state andan engaged state, the method comprising: setting the state of thetransmission as the neutral state or the engaged state based on arestart condition, the restart condition being one of: (i) a no wheeltorque restart condition, and (ii) a wheel torque restart condition; andstarting the engine.
 2. The method of claim 1 further comprising:stopping the engine in response to a shutdown condition.
 3. The methodof claim 1, wherein the wheel torque restart condition is an operatoraction which demands wheel torque.
 4. The method of claim 3 whereinsetting the state of the transmission further comprises: setting thestate of the transmission as the engaged state in response to the wheeltorque restart condition.
 5. The method of claim 4 wherein the operatoraction which demands wheel torque comprises: an operator release of abrake pedal.
 6. The method of claim 4 wherein the operator action whichdemands wheel torque comprises: an actuation of an accelerator pedal. 7.The method of claim 1, wherein the no wheel torque restart condition isa system condition which demands engine power without demanding wheeltorque.
 8. The method of claim 7 wherein setting the state of thetransmission further comprises: setting the state of the transmission asthe neutral state in response to the no wheel torque restart condition.9. The method of claim 8 wherein the transmission has an active neutralstate and a full neutral state, and wherein setting the state of thetransmission further comprises: setting the state of the transmission asthe active neutral state.
 10. The method of claim 8 wherein thetransmission has an active neutral state and a full neutral state, andwherein setting the state of the transmission further comprises: settingthe state of the transmission as the full neutral state.
 11. A method ofstarting a vehicle engine comprising: setting a transmission state basedon a restart condition, the restart condition being one of: (i) arestart condition corresponding with a system condition which demandsengine power without demanding wheel torque, and (ii) a restartcondition corresponding with a driver torque request; and starting theengine.
 12. The method of claim 11 further comprising: stopping theengine in response to a shutdown condition.
 13. A method of controllinga vehicle having an engine and a transmission with a neutral state andan engaged state, the method comprising: shifting the transmission intothe neutral state or the engaged state in response to a restartcondition corresponding to one of: (i) a no wheel torque restartcondition, and (ii) a wheel torque restart condition; and starting theengine.
 14. The method of claim 13, wherein shifting the transmissioninto the neutral state or the engaged state in response to a restartcondition includes shifting the transmission into the engaged state inresponse to a driver torque request.
 15. The method of claim 14, whereinthe driver torque request is a driver release of a brake pedal.
 16. Themethod of claim 14, wherein the driver torque request is a driveractuation of an accelerator pedal.
 17. The method of claim 13, whereinshifting the transmission into the neutral state or the engaged state inresponse to a restart condition includes shifting the transmission intothe neutral state in response to a system condition which demands enginepower without demanding wheel torque.
 18. The method of claim 17,wherein the transmission has a full neutral state and an active neutralstate and shifting the transmission into the neutral state comprisesshifting the transmission into the full neutral state.
 19. The method ofclaim 17, wherein the transmission has a full neutral state and anactive neutral state and shifting the transmission into the neutralstate comprises shifting the transmission into the active neutral state.